Dry scrubbing in a dry cleaner involves injecting hot exhaust gases from a process with a dry sorbent to capture acid gases, metals, and semi-volatile organic compounds. In most cases, it involves the injection of sodium-based or lime-based minerals such as sodium bicarbonate or hydrated lime to capture acid gases such as HCl, HF, HBr, HI, and SOx.

The capture of heavy metals and semi-volatile organic compounds can be achieved simultaneously with acid gas capture or in a separate stage through the injection of lignite coke or activated carbon.

Dry scrubbers are primarily used to remove acid gases from combustion sources. Typically, this is done by injecting a series of dry reactants to rapidly quench the gas and render the pollutants ineffective. This task is accomplished in three steps: gas cooling, reactant injection, and filtration.

Firstly, gas cooling must be performed to prepare the exhaust gases. In the gas cooling system, the emission gases are cooled to facilitate the removal of pollutants and other toxins from the gas stream. The exhaust gas is diluted using an evaporative cooler. Once the gas has been significantly cooled, the reactant injection can begin. In this step, the actual removal of harmful components from the gas takes place.

The components of the dry reactant are typically selected for their neutralizing properties, with sodium bicarbonate being frequently included. Various powders are combined and fired into the exhaust gas at high pressures.

Chemical reactions occur that reduce the gas’s acidity and remove harmful pollutants. The final step is to use a dust collector to capture the spent scrubbing powder as the cleaned gas exits the scrubbing chamber.

This spent powder can sometimes be cleaned and reused for dry scrubbing, but it often needs to be disposed of as it cannot be adequately washed.